The present invention generally relates to ink compositions and delivery systems associated therewith, and more particularly to invisible ink materials which include one or more chemical agents therein that cannot be seen by the unaided eye but will fluoresce when exposed to (1) far red (xe2x80x9cFRxe2x80x9d) light; (2) infrared (xe2x80x9cIRxe2x80x9d) light; or (2) ultraviolet (xe2x80x9cUVxe2x80x9d) light, depending on the particular chemical agents being used. The resulting fluorescent emission can then be detected through the use of a suitable detection system when far red/infrared light is applied or observed by the unaided eye when ultraviolet illumination is employed. The invisible ink compositions have many uses in a variety of different fields and represent an advance in invisible imaging technology.
In recent years, the demand for effective xe2x80x9cinvisiblexe2x80x9d ink compositions has steadily increased. Invisible ink materials are traditionally defined to involve a broad class of ink formulations which cannot be seen by the unaided eye when applied to a substrate and viewed with xe2x80x9cnaturalxe2x80x9d light (e.g. light from the sun) or light from conventional incandescent lamps and the like. Both of these light forms (as well as other forms which are normally used for general illumination purposes in homes, businesses, and the like) are collectively characterized as xe2x80x9cwhitexe2x80x9d light which involves a combination of all the various colored light fractions which fall within a wavelength range of about 300-700 nm. Under these illumination conditions, the ink compositions are essentially colorless. Only after illumination with other, more narrow light wavelengths do the printed images become visible or otherwise detectible (either with or without auxiliary observation equipment).
The uses of these materials are varied and widespread. For example, invisible ink products provide many benefits when printed on a variety of documents including insurance policies, checks, and other related materials. Of particular interest is the use of invisible inks on paperwork prepared by financial institutions (e.g. checks, account statements, routing documents, and the like). These items typically contain a wide variety of routing codes, numerical identifiers, data summaries, and the like which (for numerous reasons including security-related issues) preferably remain invisible to the unaided eye under the conditions outlined above. Likewise, in many applications, it is desired that xe2x80x9cbar-codingxe2x80x9d for inventory control, product assembly applications in factories, and other comparable purposes be undertaken in a manner where the particular bar-code of interest does not appear in visible form on the products or documents being processed. Representative patents which discuss the use of invisible ink materials for bar-coding purposes include but are not limited U.S. Pat. No. 5,282,894 to Albert et al.; U.S. Pat. No. 5,348,348 to Hanada et al.; and U.S. Pat. No. 5,686,725 to Maruyama et al. Other patents which generally describe the usefulness of invisible ink materials for a variety of different purposes include U.S. Pat. No. 4,243,694 to Mansukhani; U.S. Pat. No. 4,540,595 to Acitelli et al.; U.S. Pat. No. 5,093,147 to Andrus et al.; U.S. Pat. No. 5,215,838 to Tam et al.; U.S. Pat. No. 5,301,044 to Wright; U.S. Pat. No. 5,423,432 to Krutak et al.; U.S. Pat. No. 5,614,008 to Krutak et al.; U.S. Pat. No. 5,643,356 to Nohr et al.; U.S. Pat. No. 5,684,069 to Auslander; U.S. Pat. No. 5,702,511 to de Saint-Romain et al.; U.S. Pat. No. 5,703,229 to Krutak et al., and others.
In addition to the various patents which exist involving invisible ink materials in general, a number of patents have been granted which describe specific approaches for handling and formulating invisible ink compositions. For example, certain references disclose invisible dye compounds which are xe2x80x9ccomplexedxe2x80x9d (e.g. chemically coupled or otherwise joined) with a variety of polymeric materials (see U.S. Pat. No. 5,614,008 cited above). The polymers are apparently designed to increase the fluorescence intensity of the dyes. Notwithstanding the benefits associated with this process, the presence of polymeric materials within the completed ink formulations (particularly those that are complexed with the selected dye compound[s]) can diminish print quality levels and reduce overall printer reliability in applications involving high speed/high resolution inkjet printing. This situation can occur because these polymers often form undesired films or deposits within the printing system which interfere or otherwise prevent effective ink drop formation. As a result, images with poor print quality and inadequate edge acuity are generated.
With continued reference to inkjet technology, this approach is of considerable interest in the marking of substrates using invisible inks. Inkjet printing techniques are characterized by a high degree of operational efficiency, low cost, excellent print quality, and rapid ink delivery. Thermal inkjet printing units are especially important in this regard. Printing systems which employ thermal inkjet technology basically involve a cartridge unit having at least one ink reservoir chamber in fluid communication with a printhead. The printhead includes a substrate (preferably made of silicon) that comprises a plurality of thin-film heating resistors thereon.
Selective activation of the resistors causes thermal excitation of the ink materials retained within the ink cartridge and expulsion thereof from the cartridge. Representative thermal inkjet systems are discussed in U.S. Pat. No. 4,500,895 to Buck et al.; U.S. Pat. No. 4,771,295 to Baker et al.; U.S. Pat. No. 5,278,584 to Keefe et al; and the Hewlett-Packard Journal, Vol. 39, No. 4 (August 1988), all of which are incorporated herein by reference. Further information regarding inkjet printing devices (including those which incorporate thermal inkjet technology) will be discussed below relative to the present invention.
The invention claimed herein shall be applicable to all types of inkjet printing systems including those which employ cartridge units having a self-contained supply of ink within a housing that is directly attached to a printhead, as well as alternative inkjet systems which use an ink supply that is remotely positioned from the printhead and in fluid communication therewith using one or more conduit members. The claimed materials and methods are also applicable to inkjet printing units using other (e.g. non-thermal) ink delivery methods including those which incorporate, for example, piezoelectric technology as discussed further below.
Inkjet printing techniques and the use of invisible ink materials for the purposes outlined above (and other related applications) offer many important benefits. In accordance with the specialized components employed in inkjet printing systems (particularly thermal inkjet units) which typically include numerous small openings, passageways, and the like through which ink materials must pass, the inks selected for use in these systems must be carefully considered. Otherwise, print quality deterioration and a decrease in operating efficiency can occur. In addition to these factors, the ink materials of interest must comply with many other requirements including high levels of waterfastness, lightfastness, fluorescence intensity, bleed resistance, and the like. The present invention involves specialized invisible ink compositions which are particularly well-suited for use in inkjet printing systems (especially those which employ thermal inkjet technology). Likewise, the materials and methods described herein overcome numerous problems associated with prior invisible ink formulations and offer many advantages including but not limited to (1) high print quality levels (particularly when thermal inkjet technology is employed); (2) superior lightfastness and waterfastness; (3) excellent fluorescence intensity during illumination with an appropriate light source; and (4) a high level of reliability when used in connection with inkjet printing systems (particularly those which employ thermal inkjet technology).
Accordingly, the present invention represents an advance in the art of invisible ink imaging which satisfies a long-felt need as noted above. It will become readily apparent from the following discussion that the invention is novel in the materials and procedures that it employs, as well as the results which it obtains. The claimed invention therefore constitutes a unique development of considerable significance which will now be discussed in detail.
It is an object of the present invention to provide a novel invisible ink composition which contains a highly sensitive fluorophoric compound that cannot be seen by the unaided eye but fluoresces with considerable intensity when illuminated with far red (xe2x80x9cFRxe2x80x9d) or infrared (xe2x80x9cIRxe2x80x9d) light (characterized herein as a far red/infrared fluorophore or fluorophoric compound).
It is another object of the invention to provide a novel invisible ink composition which contains a highly sensitive far red/infrared fluorophoric compound that is uncomplexed with any polymeric additives or other ingredients.
It is another object of the invention to provide a novel invisible ink composition which, in an-alternative embodiment, likewise contains (in combination with the far red/infrared fluorophore) an ultraviolet fluorophoric compound which cannot be seen by the unaided eye but fluoresces with considerable intensity when illuminated with ultraviolet (xe2x80x9cUVxe2x80x9d) light.
It is another object of the invention to provide a novel invisible ink composition which is highly suitable for use with inkjet printing systems (especially those that employ thermal inkjet technology).
It is another object of the invention to provide a novel invisible ink composition which is waterfast, lightfast, and capable of producing high resolution printed images.
It is another object of the invention to provide a novel invisible ink composition in which the fluorophoric materials therein have fluorescent properties that enable them to be readily observed using a minimal amount of detection equipment.
It is another object of the invention to provide a novel invisible ink composition which is capable of being used in a highly reliable manner with a wide variety of printing systems.
It is another object of the invention to provide a novel invisible ink composition which provides the foregoing benefits while using a minimal number of chemical ingredients.
It is a further object of the invention to provide a novel invisible ink composition which is able to form clear and distinct printed images on a wide variety of substrates, with xe2x80x9cspecialxe2x80x9d substrates not being required.
It is a further object of the invention to provide a novel invisible ink composition which is suitable for use in many different applications, environments, and situations.
It is a still further object of the invention to provide a novel printing method which employs the invisible ink materials described above.
It is a still further object of the invention to provide a novel printing method which employs the invisible ink materials described above wherein inkjet technology is used to generate printed images.
It is an even further object of the invention to provide a novel printing method which employs the invisible ink materials described above in a thermal inkjet printing apparatus.
It is an even further object of the invention to provide a novel printing method which employs the invisible ink materials described above that is rapid, accurate, and reliable with a high level of print quality.
A brief summary of the invention and its benefits will now be provided, with specific details thereof being recited in the Detailed Description of Preferred Embodiments section. The present invention involves a highly effective invisible ink composition and image generation method which can be used in many different environments. In particular, the various embodiments of the claimed ink composition are able to generate printed images on a selected substrate (including paper materials) which cannot be seen by the unaided eye when applied to a substrate and viewed with xe2x80x9cnaturalxe2x80x9d light (e.g. light from the sun) or light from conventional incandescent lamps and the like. Both of these light forms (as well as other forms which are normally used for general illumination purposes in homes, businesses, and the like) are collectively characterized as xe2x80x9cwhitexe2x80x9d light which involves a combination of all the various colored light fractions which fall within a wavelength range of about 300-700 nm. Under these illumination conditions, the ink compositions are essentially colorless. Only after illumination with other, more narrow light wavelengths do the printed images become visible to the observer (either with or without auxiliary observation equipment).
To observe the xe2x80x9cinvisiblexe2x80x9d printed images, they must be illuminated with either far red or infrared light (e.g. light within an optimal and non-limiting wavelength range of about 650-715 nm which encompasses both the far red and infrared wavelengths of primary interest) or ultraviolet (xe2x80x9cUVxe2x80x9d) light (e.g. light within an optimal and non-limiting wavelength range of about 250-380 nm), depending on the particular embodiment under consideration. Regardless of the specific embodiment selected for use in a given situation, the ink compositions described herein (and printing methods associated therewith) enable printed images to be generated with a high level of image quality while avoiding the difficulties experienced by conventional invisible inks. Polymeric additives or xe2x80x9ccomplexing agentsxe2x80x9d are not required in the ink formulations discussed below, with the claimed dye compounds being characterized as xe2x80x9cuncomplexedxe2x80x9d. The term xe2x80x9cuncomplexedxe2x80x9d as used herein shall involve a situation in which the dyes of interest are not chemically linked to any particular materials (especially polymeric compounds) and do not form any dye xe2x80x9ccomplexesxe2x80x9d. As a result, the overall ability of the inks to function effectively in many different printing systems with high reliability levels is increased. This is particularly true when thermal inkjet systems are employed to generate invisible images in a high-speed manner with minimal xe2x80x9cdown-timexe2x80x9d. Additional benefits and specific information regarding the ink formulations and printing methods of the invention will be presented in the Detailed Description of Preferred Embodiments section, with the claimed products and processes representing a considerable advance in the art of invisible imaging technology.
In a primary embodiment of the invention, an ink composition is provided which includes an invisible dye comprising an uncomplexed invisible metal phthalocyanine fluorophore of the far red/infrared variety which is optimally water-soluble. Materials that are xe2x80x9cinvisiblexe2x80x9d as discussed herein involve compositions which cannot be seen by the unaided eye under the conditions expressed above. The term xe2x80x9cfluorophorexe2x80x9d generally involves a chemical composition which is capable of absorbing light and thereafter emitting fluorescent light upon excitation with light of a given wavelength. Phthalocyanines (as a group) are basically defined to include four isoindole groups (e.g. [(C6H4)C2N]) which are linked together to form a complex conjugated structure. Metal phthalocyanine materials contain one or more metal atoms therein which are strategically located in the phthalocyanine structure. The term xe2x80x9cuncomplexedxe2x80x9d is defined above and encompasses metal phthalocyanine compounds that are not chemically linked with any other materials (including organic polymers) to form complex molecules as used in prior systems such as those discussed in U.S. Pat. No. 5,614,008. Of primary interest in this case is the use of a novel uncomplexed invisible aluminum phthalocyanine fluorophore, with further information regarding this composition being provided below.
As previously noted, the use of dye-polymer complexes can present reliability and image-quality problems in systems which, for example, employ thermal inkjet technology on a high-speed/high resolution basis (e.g. at least about 600 dpi [xe2x80x9cdots-per-inchxe2x80x9d] at a frequency of about 12-16 kHz or more). The use of an invisible metal (e.g. aluminum) phthalocyanine fluorophoric dye composition that is uncomplexed and employed in a xe2x80x9cfreexe2x80x9d state in connection with the wavelength ranges specified herein represents a novel advance in the art of invisible ink imaging, especially in connection with thermal inkjet technology.
While the present invention in its broadest sense shall not be restricted to any specific uncomplexed invisible metal phthalocyanine far red/infrared fluorophores, it has been discovered that unexpectedly superior results (in terms of image quality, waterfastness, lightfastness, reliability, fluorescence intensity, and the like) are achieved through the use of a special water-soluble uncomplexed aluminum phthalocyanine far red/infrared fluorophore. This particular material shall be designated herein as xe2x80x9cchloroaluminum (III) phthalocyanine tetrasulfonic acidxe2x80x9d (or salts thereof) which (in the acid form) involves the following structural formula: 
From a nomenclature standpoint, the above-listed composition consists of C32H16AlClN8O12S4, with the following xe2x80x9clong-handxe2x80x9d name being applicable: chloro[29H,31H-phthalocyanine-2,9,17,24-tetrasulphonato (6-) -N29,N30,N32]-aluminate(4-). As shown in the foregoing formula, four (xe2x80x94SO3H) groups are provided. To form salts of this compound, the hydrogen ions in one or more of the (xe2x80x94SO3H) groups (e.g. 1-4 of the groups) may be replaced with a positive counterion preferably selected from the group consisting of lithium (Li+) sodium (Na+), potassium (K+), rubidium (Rb+), calcium (Ca+2), magnesium (Mg+2), aluminum (Al+3), ammonium (NH4+), and water-soluble ammonium compounds such as the methyl, ethyl, and ethoxy derivatives thereof. All of the selected counterions may be the same when more than one of the (xe2x80x94SO3H) groups is involved or mixtures of different counterions can be employed. A representative and non-limiting example of a salt of the above-listed composition (e.g. sodium chloroaluminum [III] phthalocyanine tetrasulfonate) is provided as follows: 
Again, many different salts are possible (along with varying xe2x80x9csaturationxe2x80x9d levels associated with the [SO3xe2x88x921] groups shown above.) Chloroaluminum (III) phthalocyanine tetrasulfonic acid and salts thereof are commercially available from the Ciba-Geigy Corp. of Charlotte, N.C. (USA)/Basel Switzerland under the name xe2x80x9cTINOLUX BBSxe2x80x9d or xe2x80x9ctetrabenzo tetraazaporphinexe2x80x9d. Likewise, in a preferred and non-limiting embodiment, the completed ink composition will contain about 1-200 ppm or about 0.0001-0.02% by weight of the invisible dye material (e.g. the uncompleted invisible metal far red/infrared phthalocyanine fluorophore with particular reference to chloroaluminum [III] phthalocyanine tetrasulfonic acid and salts thereof).
The uncompleted invisible metal phthalocyanine far red/infrared fluorophoric dye compositions discussed above (including chloroaluminum [III] phthalocyanine tetrasulfonic acid/salt materials) cannot be seen with the unaided eye (e.g. are xe2x80x9cinvisiblexe2x80x9d) as defined above. However, in accordance with the fluorophoric character thereof, such materials will fluoresce with a high degree of intensity (discussed below) when illuminated with far red or infrared light having a wavelength sufficient to cause such fluorescence (light within an optimal, non-limiting wavelength range of about 650-715 nm which encompasses both the far red and infrared wavelengths of primary interest). This flourescent emission can then be detected and otherwise characterized (observed) using a suitable detection/observation system. Fluorescent emission associated with the foregoing far red/infrared fluorophores (e.g. the specific and general materials listed above) will optimally involve the generation of light within a wavelength range of about 670-720 nm). This light is not visible with the unaided eye and can be detected using suitable detection devices as specified below.
The claimed ink composition will likewise comprise at least one ink xe2x80x9cvehiclexe2x80x9d which may include a number of different ingredients in combination. In a preferred embodiment, the ink vehicle will comprise (1) water; (2) at least one organic solvent material (which may also function as a xe2x80x9chumectantxe2x80x9d, namely, a moisture-retaining agent); or preferably mixtures thereof with these compositions being present in varied proportions as further discussed in the Detailed Description of Preferred Embodiments section. Exemplary and preferred organic solvents/vehicles suitable for use in the claimed ink composition include but are not limited to 2-pyrrolidone; ethoxylated glycerol; diethylene glycol; tetraethylene glycol; 1,5-pentanediol; 1,3-propanediol; N-methyl pyrrolidone; 2-propanol; 2-ethyl-2-hydroxymethyl-1,3-propanediol; and mixtures thereof. At this point, it should be emphasized that the present invention and its various embodiments shall not be restricted to any particular compositions, materials, proportions, amounts, and other parameters unless otherwise stated herein. All numerical values and ranges provided in this description are recited for example purposes only and shall constitute preferred embodiments of the invention designed to achieve maximum operational efficiency. As a final note regarding the ink compositions of interest, they may include a number of supplemental (e.g. optional) ingredients outlined in considerable detail below including without limitation surfactants, additional humectants (defined above), biocides, buffering agents, and the like. Specific and detailed examples of preferred ink formulations will again be presented in the following Detailed Description of Preferred Embodiments section.
In a second embodiment, an alternative ink composition is provided which includes all of the ingredients listed in connection with the first embodiment (including the uncomplexed invisible metal phthalocyanine far red/infrared fluorophore as a general class of materials and the preferred composition recited above [chloroaluminum (III) phthalocyanine tetrasulfonic acid or salts thereof]). Accordingly, the previous discussion involving the first ink composition shall be incorporated by reference relative to the second ink composition now being described. The main difference between both ink formulations involves the addition of a second invisible dye composition to the alternative ink product, with the second dye comprising at least one invisible ultraviolet fluorophore which cannot be seen by the unaided eye in xe2x80x9cwhitexe2x80x9d light or other comparable light forms as discussed above. However, when ultraviolet light is applied (e.g. light within an optimum, non-limiting wavelength range of about 250-380 nm), the ultraviolet fluorophore will fluoresce in a visible manner (e.g. within an optimum, non-limiting wavelength range of about 400-650 nm) and is thereby observable with the unaided eye. Incidentally, in this embodiment, the invisible ultraviolet fluorophore discussed above shall be designated herein as a xe2x80x9csecond invisible dyexe2x80x9d, with the uncompleted invisible metal phthalocyanine far red/infrared fluorophore being characterized as a xe2x80x9cfirst invisible dyexe2x80x9d.
This embodiment shall not be restricted to any particular quantities in connection with both of the above-listed fluorophores (which may be determined in accordance with routine preliminary pilot testing). However, optimum results are achieved if the ink composition contains about 1-200 ppm or about 0.0001-0.02% by weight total combined first invisible dye (e.g. the uncompleted invisible metal phthalocyanine far red/infrared fluorophore as a general class of materials and the preferred composition recited above [chloroaluminum (III) phthalocyanine tetrasulfonic acid or salts thereof]) and about 500-50000 ppm or about 0.05-5% by weight total combined second invisible dye, namely, the claimed ultraviolet fluorophore[s]. While a number of different ultraviolet fluorophores may be used in connection with the second invisible dye without limitation, exemplary and preferred materials suitable for this purpose include but are not limited to ultraviolet absorbing stilbenes, pyrazolines, coumarins, carbostyrils, pyrenes, and mixtures thereof. Representative materials in each of these classes are as follows: (1) stilbenes: 4,4xe2x80x2-bis(triazin-2-ylamino)stilbene-2,2xe2x80x2-disulfonic acid; benzenesulfonic acid-2,2xe2x80x2-(1,2-ethenediyl)bis[5-[4-bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2yl]amino-tetrasodium salt; and 4,4-bis [4-diisopropanolamino-6-(p-sulfoanilino)-s-triazin-2-yl-amine]stilbene-sodium disulfonate; (2) pyrazolines: 1,2-diphenyl-2-pyrazoline; (3) coumarins: 7-diethylamino-4-methylcoumarin; 7-hydroxy-4-methylcoumarin; and 3-(2-benzimidazolyl)-7-(diethylamino)coumarin; (4) carbostyrils: 2-hydroxyquinoline; and (5) pyrenes: N-(1-pyrenebutanoyl)cysteic acid. Also of interest as an ultraviolet fluorophore is dibenzothiophene-5,5-dioxide, as well as C.I. (Color Index) Fluorescent Brightener 28; C.I. Fluorescent Brightener 220; and C.I. Fluorescent Brightener 264, with some or all of these C.I. compositions being comparable or structurally equivalent to the specific materials listed above. The foregoing ultraviolet fluorophores and others are commercially available from numerous sources including but not limited to the Aldrich Chemical Co. of Milwaukee, Wis. (USA); Bayer Corporation of Pittsburgh, Pa. (USA) under the names xe2x80x9cBLANKOPHORExe2x80x9d or xe2x80x9cPHORWHITExe2x80x9d; Ciba-Geigy Corporation of Greensboro, N.C. (USA)/Basil, Switzerland; Molecular Probes of Eugene, Oreg. (USA); Sandoz Chemicals of Charlotte, N.C. (USA) under the name xe2x80x9cLEUKOPHORxe2x80x9d; and Sigma Co. of St. Louis, Mo. (USA). These materials are characterized by their ability to generate fluorescent light upon ultraviolet illumination as discussed herein which can be seen by the unaided eye.
This alternative embodiment of the claimed ink composition will likewise comprise a number of additional materials therein, all of which are substantially the same as those listed above in connection with the first embodiment. For example, at least one ink xe2x80x9cvehiclexe2x80x9d will be employed which may include a number of different ingredients in combination. In a preferred embodiment, the ink vehicle will again comprise (1) water; (2) at least one organic solvent material (which may also function as a xe2x80x9chumectantxe2x80x9d, namely, a moisture-retaining agent); or preferably mixtures thereof, with these compositions being present in varied proportions. Exemplary and preferred organic solvents/vehicles suitable for use in the claimed second ink composition include but are not limited to 2-pyrrolidone; ethoxylated glycerol; diethylene glycol; tetraethylene glycol; 1,5-pentanediol; 1,3-propanediol; N-methyl pyrrolidone; 2-propanol; 2-ethyl-2-hydroxymethyl-1,3-propanediol; and mixtures thereof. As a final note regarding the ink formulations associated with this embodiment, they may again contain a number of supplemental (e.g. optional) ingredients outlined in considerable detail below including without limitation surfactants, additional humectants, biocides, buffering agents, and the like.
Having described the ink compositions of primary interest in this case and their main components, preferred printing methods using the specialized ink products of the invention will now be summarized. Basically, the inks may be delivered using a wide variety of printing systems without limitation. However, in a preferred embodiment, the claimed inks are particularly suitable for delivery using inkjet printing units (especially those which employ thermal inkjet technology). This suitability is based on the particular ingredients chosen for use in the ink compositions (especially the uncomplexed invisible metal phthalocyanine far red/infrared fluorophore, namely, chloroaluminum [III] phthalocyanine tetrasulfonic acid or salts thereof). The following discussion shall therefore focus on the use of inkjet technology to deliver the claimed ink compositions to a selected substrate with the understanding that the inks described herein may also be transferred using other diverse printing techniques ranging from silkscreen methods to conventional offset processes.
To produce a printed invisible image using the selected ink formulations, an ink delivery system is initially provided. In a preferred embodiment, the ink delivery system will generally be configured in the form of an ink cartridge unit (mounted within a suitable printer) which includes a housing having at least one ink-retaining chamber inside. The ink-retaining chamber will contain a supply of invisible ink therein corresponding to either of the two embodiments listed above. In this regard, the printing method currently being described is equally applicable to all of the ink compositions discussed herein. These compositions again include (1) the product of the first embodiment in which the ink composition contains [A] an invisible dye comprising an uncompleted invisible metal phthalocyanine far red/infrared fluorophore (with chloroaluminum [III] phthalocyanine tetrasulfonic acid or salts thereof providing optimum results); and [B] an ink vehicle comprising water and/or at least one organic solvent, and (2) the product of the second embodiment in which the ink composition contains [A] a first invisible dye comprising an uncomplexed invisible metal phthalocyanine far red/infrared fluorophore (with chloroaluminum [III] phthalocyanine tetrasulfonic acid or salts thereof again providing optimum results); [b] a second invisible dye comprising an ultraviolet fluorophore; and [c] an ink vehicle comprising water and/or at least one organic solvent. Specific information regarding these ink materials is listed above (including the optimal absorption/emission wavelength characteristics thereof), with this information being incorporated by reference in the present discussion of preferred printing methods. In particular, it is important to note that the selected uncomplexed invisible metal phthalocyanine far red/infrared fluorophore will optimally absorb light within a wavelength range of about 650-715 nm and emit fluorescent light within a wavelength range of about 670-720 nm. Likewise, in the second embodiment of the claimed ink composition, the ultraviolet fluorophore will optimally absorb light within a wavelength range of about 250-380 nm and emit light within a wavelength range of about 400-650 nm.
The ink delivery system also includes a printhead in fluid communication with the ink-retaining chamber and ink materials in the housing, with the printhead comprising at least one ink ejector for expelling ink on-demand from the ink-retaining chamber. In an exemplary and preferred embodiment involving the use of a thermal inkjet apparatus, the printhead will include a plurality of resistors and an outer plate having at least one or more ink ejection openings through the plate.
Next, a substrate is provided which is designed to receive the invisible ink. The present invention shall not be limited to any particular substrates, with a wide variety of materials being applicable for this purpose including substrates made from paper, metal, plastic, and the like. It is an important attribute of the claimed ink formulations and methods that xe2x80x9cspecialsxe2x80x9d substrates (including custom-produced paper products) are not required.
To initiate the printing process, the printhead of the ink delivery system is activated in order to deliver the chosen invisible ink composition from the ink retaining chamber of the housing onto the substrate. Activation of the printhead in a thermal inkjet system will involve selective energization of the resistors in order to heat the ink and thereby expel it from the ink retaining chamber. If non-thermal-inkjet systems are used to deliver the ink, printhead activation will be accomplished using the particular ink ejectors under consideration, with the procedures associated therewith varying from system to system. It should also be understood that the printing process discussed above is equally applicable to (A) systems in which the inkjet printhead is directly attached to the housing in order to form an integral, self-contained cartridge unit having a supply of ink within the housing; and (B) systems in which the housing and ink materials therein are remotely positioned from the printhead and in fluid communication therewith using one or more tubular conduits. In this regard, any statements which indicate that the printhead is in xe2x80x9cfluid communicationxe2x80x9d with or xe2x80x9coperatively connected toxe2x80x9d the ink retaining chamber and housing shall encompass both of the foregoing variations.
In accordance with the steps described above, a printed image is generated on the substrate which is not visible to the unaided eye in xe2x80x9cnormalxe2x80x9d or xe2x80x9cwhitexe2x80x9d light as discussed herein, with the image thus being characterized as xe2x80x9cinvisiblexe2x80x9d. As a result, the printed image is highly useful in security-related applications. When detection of the image is desired (and the ink composition of the first embodiment is employed which contains a selected invisible far red/infrared fluorophore), light is applied having a wavelength sufficient to cause the printed image to emit fluorescent light. In order to achieve optimum results in this embodiment (which again involves the use of an invisible far red/infrared fluorophore including but not limited to chloroaluminum [III] phthalocyanine tetrasulfonic acid or salts thereof), either far red or infrared light is applied to the image. In a preferred embodiment, light within an optimal, non-limiting wavelength range of about 650-715 nm is used which encompasses both the far red and infrared wavelengths of primary interest. Within this range, best results may be achieved using a non-limiting wavelength range of about 660-690 nm. The application of light in this manner will cause the ink composition to fluoresce within an optimal, non-limiting wavelength range of about 670-720 (best=about 670-710 nm). A high fluorescence level is achieved using the uncomplexed invisible metal phthalocyanine far red/infrared fluorophore compositions described herein (particularly chloroaluminum [III] phthalocyanine tetrasulfonic acid/salt materials which provide unexpectedly superior results). The resulting fluorescent emission from the printed image (which is not visible to the unaided eye) may then be detected or otherwise observed using a suitable infrared fluorescence detecting system to be discussed in greater detail below.
In an alternative embodiment, the invisible printed image can be produced from an ink composition which has (A) the first invisible dye (e.g. the uncomplexed invisible metal phthalocyanine far red/infrared fluorophore with particular emphasis on chloroaluminum [III] phthalocyanine tetrasulfonic acid and salts thereof); and (B) the second invisible dye, namely, an invisible ultraviolet fluorophore. As previously noted, the image generated from this dual-fluorophore ink composition will likewise be invisible to the unaided eye when viewed under xe2x80x9cnormalxe2x80x9d or xe2x80x9cwhitexe2x80x9d light as previously indicated. When observation/detection of the image is desired, light of a predetermined wavelength is applied to the invisible printed image which again has a wavelength sufficient to cause the printed image to generate fluorescent light. The light which may be employed for this purpose includes: (1) either far red or infrared light which, in a preferred embodiment, will involve an optimal, non-limiting wavelength range of about 650-715 nm which encompasses both the far red and infrared wavelengths of primary interest, with best results being achieved at about 66014 690 nm; and/or (2) ultraviolet light within a preferred and non-limiting wavelength range of about 250-380 nm. The application of light in this manner will cause the ink composition to fluoresce in a highly effective manner. Specifically, if far red or infrared light is applied (e.g. within the foregoing range), fluorescent light will be emitted within an optimal, non-limiting wavelength range of about 670-720 nm (best=about 670-710 nm). This emitted light (which is not visible to the unaided eye) may then be detected or otherwise observed using a suitable infrared fluorescence detecting system to be discussed in greater detail below.
If ultraviolet light is applied (e.g. within the foregoing range), fluorescent light will be emitted within an optimal, non-limiting wavelength range of about 400-650 nm. As a result, the printed image may be seen with the unaided eye and special observation or detecting equipment is not required. Likewise, the unique nature of this xe2x80x9ccombinedxe2x80x9d FR/IR/UV fluorophore system will become readily apparent from the specific information provided below.
In a system where far red/infrared light and ultraviolet light are applied in combination to a printed image containing both of the fluorophores listed above, the results will involve a combination of the effects described above. Specifically, a xe2x80x9cdual emissionxe2x80x9d situation will exist involving fluorescent light from both fluorophores which can be observed using either of the previously described techniques. The selection of any given technique (either an appropriate detecting system or the unaided eye) will depend on whether the emission being observed is from the far red/infrared fluorophore or the ultraviolet fluorophore.
A decision to employ an ink composition containing an uncomplexed invisible metal phthalocyanine far red/infrared fluorophore (particularly chloroaluminum [III] phthalocyanine tetrasulfonic acid or salts thereof) by itself or combined with an ultraviolet fluorophore will depend on the intended use of the marking system. For example, the combined FR/IR/UV fluorophore technique provides the following benefits: (1) a high degree of flexibility which enables users of the system to employ either a far red/infrared or ultraviolet light source with a single ink composition; and (2) an enhanced level of security by requiring readability in two different wavelength regions. Regardless of which ink formulation is selected for use, the present invention represents a considerable advance in the art of invisible ink imaging. In particular, the claimed inks and printing methods provide many important benefits compared with previously known techniques including a high degree of simplicity, applicability to a wide variety of printing systems with emphasis on thermal inkjet technology, cost-efficiency, superior print quality/uniformity, excellent stability (namely, lightfastness and waterfastness), and the general ability to produce completely invisible images which are readily detected on-demand by the application of far red, infrared, and/or ultraviolet light thereto.
The summary presented above was designed to offer a brief overview of the invention and shall not limit the scope thereof in any manner. A more detailed, fully-enabling, and comprehensive assessment of the invention including a discussion of the claimed inks and printing techniques will now be provided. Accordingly, these and other objects, features, and advantages of the invention shall be set forth below in the Detailed Description of Preferred Embodiments.